31Ethernet link aggregation configurationOverviewEthernet link aggregation, or simply link aggregation, combines multiple physical Ethernet ports into onelogical link, called an “aggregate link”. Link aggregation delivers the following benefits:• Increases bandwidth beyond the limits of any single link. In an aggregate link, traffic is distributedacross the member ports.• Improves link reliability. The member ports dynamically back up one another. When a member portfails, its traffic is automatically switched to other member ports.As shown in Figure 8, Device A and Device B are connected by three physical Ethernet links. Thesephysical Ethernet links are combined into an aggregate link, Link Aggregation 1. The bandwidth of thisaggregate link is as high as the total bandwidth of the three physical Ethernet links. At the same time, thethree Ethernet links back up one another.Figure 8 Ethernet link aggregationBasic conceptsAggregation group, member port, aggregate interfaceLink aggregation is implemented through link aggregation groups. An aggregation group is a group ofEthernet interfaces combined together, which are called “member ports” of the aggregation group. Foreach aggregation group, a logical interface, called an “aggregate interface”, is created.NOTE:The rate of an aggregate interface equals the total rate of its member ports in the Selected state, and itsduplex mode is the same as the selected member ports. For more information about the states of memberports in an aggregation group, see “Aggregation states of member ports in an aggregation group.”Aggregation states of member ports in an aggregation groupA member port in an aggregation group can be in either of the following aggregation states:• Selected: A Selected port can forward user traffic.• Unselected: An Unselected port cannot forward user traffic.Operational keyWhen aggregating ports, the system automatically assigns each port an operational key based on portinformation such as port rate and duplex mode. Any change to this information triggers a recalculationof the operational key.In an aggregation group, all selected member ports are assigned the same operational key.
